1. Field of the Invention
The present invention relates generally to trenching assemblies, and in particular to trenching tool assemblies for the high speed trenching of highway surfaces.
2. Description of Related Art
Machines used for trenching concrete, asphalt, rock and the like generally include a plurality of bits rigidly mounted on a rotating mechanism which impacts the bits against the surface. The driven mechanism carrying the bits may be a rotating drum, disk, or a continuous flexible chain for example. Owing to the nature of the materials being trenched, extremely high impact forces are required to be transmitted by the bits. Even greater impact forces are experienced by the bits as the trenching machines are designed to be operated at higher speeds to increase the cutting rate of the machines. As a result, the bits wear quickly and must be frequently replaced. If the machine is to be operated efficiently, the rate of bit wear must be minimized, and bit replacement must be simple and quick.
Bits and bit mounting assemblies have been developed to rigidly mount the bit and mounting block to a rotating drum to withstand the extremely high impact forces, while allowing for ready replacement, such as that disclosed in U.S. Pat. No. 4,337,980 to Krekeler, for example. Another design, incorporated in the Fansteel 765 Series bits available from VR/Wesson Lexington, utilizes an expandable collar fitted around the shank of a bit, and which expands into a recess formed in the mounting block to secure the bit in place. As drum rotation speeds and impact forces increase, however, these known methods of mounting bits on the drum become less satisfactory due to their inability to counter the high centrifugal forces urging the bits out of the mounting blocks at high drum rotation speeds, while at the same time minimizing the damage to the bit from the accompanying high impact forces.
A need remains therefore for a trenching bit and mounting block assembly which allows the bit to enjoy a suitably long life, retains the bit within the mounting block at very high drum rotational speeds, and which allows quick and easy replacement of bits when required.